syncdata command

""" Django command similar to 'loaddata' but also deletes.
    After 'syncdata' has run, the database will have the same data as the fixture - anything
    missing will of been added, anything different will of been updated,
     and anything extra will of been deleted.
"""

from django.core.management.base import BaseCommand
from django.core.management.color import no_style
from optparse import make_option
import sys
import os

class Command(BaseCommand):
    'syncdata command'
    option_list = BaseCommand.option_list + (
        make_option('--verbosity', action='store', dest='verbosity', default='1',
            type='choice', choices=['0', '1', '2'],
            help='Verbosity level; 0=minimal output, 1=normal output, 2=all output'),
    )
    help = 'Makes the current database have the same data as the fixture(s), no more, no less.'
    args = "fixture [fixture ...]"
    
    def remove_objects_not_in(self, objects_to_keep, verbosity):
        """
        Deletes all the objects in the database that are not in objects_to_keep.
        - objects_to_keep: A map where the keys are classes, and the values are a
         set of the objects of that class we should keep.
        """
        for class_ in objects_to_keep.keys():

            current = class_.objects.all()
            current_ids = set( [x.id for x in current] )
            keep_ids = set( [x.id for x in objects_to_keep[class_]] )

            remove_these_ones = current_ids.difference(keep_ids)
            if remove_these_ones:

                for obj in current:
                    if obj.id in remove_these_ones:
                        obj.delete()
                        if verbosity >= 2:
                            print "Deleted object: "+ unicode(obj)

            if verbosity > 0 and remove_these_ones:
                num_deleted = len(remove_these_ones)
                if num_deleted > 1:
                    type_deleted = unicode(class_._meta.verbose_name_plural)
                else:
                    type_deleted = unicode(class_._meta.verbose_name)

                print "Deleted "+ str(num_deleted) +" "+ type_deleted

    def handle(self, *fixture_labels, **options):
        'Main method of a Django command'
        from django.db.models import get_apps
        from django.core import serializers
        from django.db import connection, transaction
        from django.conf import settings

        self.style = no_style()

        verbosity = int(options.get('verbosity', 1))
        show_traceback = options.get('traceback', False)
        
        # Keep a count of the installed objects and fixtures
        fixture_count = 0
        object_count = 0
        objects_per_fixture = []
        models = set()

        humanize = lambda dirname: dirname and "'%s'" % dirname or 'absolute path'

        # Get a cursor (even though we don't need one yet). This has
        # the side effect of initializing the test database (if
        # it isn't already initialized).
        cursor = connection.cursor()

        # Start transaction management. All fixtures are installed in a
        # single transaction to ensure that all references are resolved.
        transaction.commit_unless_managed()
        transaction.enter_transaction_management()
        transaction.managed(True)

        app_fixtures = [os.path.join(os.path.dirname(app.__file__), 'fixtures') \
                        for app in get_apps()]
        for fixture_label in fixture_labels:
            parts = fixture_label.split('.')
            if len(parts) == 1:
                fixture_name = fixture_label
                formats = serializers.get_public_serializer_formats()
            else:
                fixture_name, format = '.'.join(parts[:-1]), parts[-1]
                if format in serializers.get_public_serializer_formats():
                    formats = [format]
                else:
                    formats = []

            if formats:
                if verbosity > 1:
                    print "Loading '%s' fixtures..." % fixture_name
            else:
                sys.stderr.write(
                    self.style.ERROR("Problem installing fixture '%s': %s is not a known "+ \
                                     "serialization format." % (fixture_name, format))
                    )
                transaction.rollback()
                transaction.leave_transaction_management()
                return

            if os.path.isabs(fixture_name):
                fixture_dirs = [fixture_name]
            else:
                fixture_dirs = app_fixtures + list(settings.FIXTURE_DIRS) + ['']

            for fixture_dir in fixture_dirs:
                if verbosity > 1:
                    print "Checking %s for fixtures..." % humanize(fixture_dir)

                label_found = False
                for format in formats:
                    serializer = serializers.get_serializer(format)
                    if verbosity > 1:
                        print "Trying %s for %s fixture '%s'..." % \
                            (humanize(fixture_dir), format, fixture_name)
                    try:
                        full_path = os.path.join(fixture_dir, '.'.join([fixture_name, format]))
                        fixture = open(full_path, 'r')
                        if label_found:
                            fixture.close()
                            print self.style.ERROR("Multiple fixtures named '%s' in %s. Aborting." %
                                (fixture_name, humanize(fixture_dir)))
                            transaction.rollback()
                            transaction.leave_transaction_management()
                            return
                        else:
                            fixture_count += 1
                            objects_per_fixture.append(0)
                            if verbosity > 0:
                                print "Installing %s fixture '%s' from %s." % \
                                    (format, fixture_name, humanize(fixture_dir))
                            try:
                                objects_to_keep = {}
                                objects = serializers.deserialize(format, fixture)
                                for obj in objects:
                                    object_count += 1
                                    objects_per_fixture[-1] += 1

                                    class_ = obj.object.__class__
                                    if not class_ in objects_to_keep:
                                        objects_to_keep[class_] = set()
                                    objects_to_keep[class_].add(obj.object)
                                    
                                    models.add(class_)
                                    obj.save()

                                self.remove_objects_not_in(objects_to_keep, verbosity)

                                label_found = True
                            except (SystemExit, KeyboardInterrupt):
                                raise
                            except Exception:
                                import traceback
                                fixture.close()
                                transaction.rollback()
                                transaction.leave_transaction_management()
                                if show_traceback:
                                    traceback.print_exc()
                                else:
                                    sys.stderr.write(
                                        self.style.ERROR("Problem installing fixture '%s': %s\n" %
                                             (full_path, traceback.format_exc())))
                                return
                            fixture.close()
                    except:
                        if verbosity > 1:
                            print "No %s fixture '%s' in %s." % \
                                (format, fixture_name, humanize(fixture_dir))

        # If any of the fixtures we loaded contain 0 objects, assume that an 
        # error was encountered during fixture loading.
        if 0 in objects_per_fixture:
            sys.stderr.write(
                self.style.ERROR("No fixture data found for '%s'. (File format may be invalid.)" %
                    (fixture_name)))
            transaction.rollback()
            transaction.leave_transaction_management()
            return
            
        # If we found even one object in a fixture, we need to reset the 
        # database sequences.
        if object_count > 0:
            sequence_sql = connection.ops.sequence_reset_sql(self.style, models)
            if sequence_sql:
                if verbosity > 1:
                    print "Resetting sequences"
                for line in sequence_sql:
                    cursor.execute(line)
            
        transaction.commit()
        transaction.leave_transaction_management()

        if object_count == 0:
            if verbosity > 1:
                print "No fixtures found."
        else:
            if verbosity > 0:
                print "Installed %d object(s) from %d fixture(s)" % (object_count, fixture_count)
                
        # Close the DB connection. This is required as a workaround for an
        # edge case in MySQL: if the same connection is used to
        # create tables, load data, and query, the query can return
        # incorrect results. See Django #7572, MySQL #37735.
        connection.close()